1. Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board and, more particularly, to a method for manufacturing a printed circuit board, in which a step of forming circuit patterns is improved.
2. Description of the Related Art
A subtract method is conventionally known as a method for manufacturing a printed circuit board, A method for manufacturing a through hole printed circuit board according to the subtract method will be described below. First, after drilling is performed for a copper-clad laminated to form a hole, and electroless copper plating and, if necessary, electric copperplating are performed on the entire surface of the copper-clad laminate including the hole, thereby depositing a copper plating film in the inner wall surface of the hole to form a through hole. Subsequently, a filler for protecting the through hole is filled in the through hole and on the peripheral portion of the hole, and etching resist patterns are formed on the copper plating film by a photolithography method or a tenting method. The resist patterns are used as a mask to remove portions of the copper plating film and a copper foil exposed from the mask by etching to form circuit patterns, thereby manufacturing a printed circuit board.
An operation, however, of the above subtract method is cumbersome because the method requires a large number of manufacturing steps. In addition, since a large amount of waste liquors in which copper is dissolved is produced upon etching, countermeasures against environmental pollutions such as waste liquor disposal are required to result in a high running cost. Furthermore, it is difficult to form circuit patterns having a fine line width because an undercut is formed or side etching occurs during etching.
In view of the foregoing, an additive method using no copper-clad laminate is developed. In this additive method, drilling is performed for a laminate to form a hole, and the entire surface of the laminate is subjected to a catalyst treatment. Subsequently, plating resist patterns as complementary patterns of circuit patterns to be formed are formed, and electroless copper plating is performed to deposit an electroless copper plating film on the inner wall surface of the hole and the surface of the laminate exposed from the resist patterns, thereby forming a through hole and circuit patterns. Thereafter, removal of the plating resist patterns and the catalyst layer is performed to manufacture a printed circuit board. This additive method, however, requires a special plating solution in order to improve adhesion properties between the copper plating film and the laminate. In addition, since copper tends to precipitate on portions of the laminate except for a necessary portion, it is difficult to form fine circuit patterns. Furthermore, this method also has the same problem of waste liquor disposal as the subtract method.
As a method for manufacturing a printed circuit board without producing any waste liquor, a conventional die stamp method (Published Unexamined Japanese Patent Application No. 51-126277) is known. In this method, a metal mold having a blade protruding toward the outer peripheries of protruding patterns having the same shape as circuit patterns to be formed is used, and a metal foil with an adhesive is superposed on the surface of an insulating base. The metal mold is heated or pressed at room temperature to cut the metal foil with an adhesive into the shape of the circuit patterns, and at the same time the periphery of the metal foil is pushed in and bonded to the insulating base. In this method, however, since the cutting blade is formed at the peripheries of the circuit patterns of the metal mold so as to be vertical with respect to the circuit surface, it is difficult to form fine circuit patterns. In addition, when the cutting blade wears in use, the cut circuit width becomes nonuniform. Since further use of the worn cut blade makes the blade unable to make a cut, noncircuit portions are bonded with each other. Since it is very difficult to sharpen such a dull blade because of the above-mentioned shape of the mold, the number of products manufacturable per blade is very small.
In addition, when a resin film is used as the insulating base, a cut portion is formed on the surface of the resin film upon punching by the blade of the metal mold to possibly cause poor insulation. Furthermore, when wide circuit patterns are to be formed, since the blade of the metal mold initially abuts against a copper foil, air cells are easily formed between the copper foil and the insulating base. As a result, since the air cells are not removed even when the protruding patterns of the metal mold are urged against punched portions of the copper foil, circuit patterns cannot be formed on the insulating base with high adhesion force. This method also has a problem of difficulty in micropatterning of circuit patterns.